As a picture display device to be used in place of the cathode ray tube (CRT) which constitutes the main stream at present, a variety of flat panel type display devices have been investigated. Examples of such a flat panel type display device include liquid crystal display devices (LCD), electroluminescence display devices (ELD), and plasma display devices (PDP: plasma display panels). Among others, the plasma display devices have such merits as comparative easiness of an increase in screen size and an increase in angle of visibility, excellent durability to environmental factors such as temperature, magnetism, vibration, etc., long useful life and so on, and are expected to be applied not only to wall-hung television sets for home use but also to large type information terminal apparatuses for public viewing.
The plasma display device is a display device in which a voltage is applied to discharge cells containing a discharge gas consisting of a rare gas sealed in discharge spaces, and phosphor layers in the discharge are excited by UV rays generated based on glow discharge in the discharge gas, thereby achieving emission of light. Namely, the individual discharge cells are driven based on a principle similar to that of fluorescent lamps, and a collection of a large number of discharge cells, generally, on the order of several hundreds of thousands of discharge cells constitutes a single display screen. The plasma display devices are generally classified, according to the system of application of voltage to the discharge cells, into the direct current driving type (DC type) and the alternating current driving type (AC type), which have respective merits and demerits.
The AC type plasma display device has the merit that partition walls functioning to partition the individual discharge cells in the display screen may be formed in a stripe form, and is therefore suitable for increasing the definition or fineness. Besides, since the surfaces of the electrodes for discharge are covered with a dielectric layer, the electrodes would not easily be worn, which leads to the merit of long life.
In the AC type plasma display devices commercialized at present, a dielectric layer is provided on sustaining electrodes formed on the inside surface of a first substrate and the dielectric layer is generally constituted of a glass formed by paste printing and firing. In the AC type plasma display device, electric charges are accumulated on the surface of the dielectric layer, and a reverse voltage is applied to the electrodes, whereby the accumulated electric charges are released, to generate a plasma. UV rays are generated by this electric discharge, and the phosphors are excited by the UV rays, to be used for display. In addition, a protective film is provided on the inside surface of the dielectric layer on the side of the discharge spaces.
However, in the AC type plasma display device with the dielectric layer formed by the paste printing method, there is the problem of deterioration of the protective film. As for the causes of the deterioration, it is considered that the film quality of the dielectric layer formed between the protective film and the sustaining electrodes plays an important role. Namely, when the trap density of the dielectric layer is high, electrons or holes are trapped by the traps, to generate an electric potential. Particularly, it is known that in a silicon oxide based dielectric layer, many electron traps due to OH groups are generated. The traps due to the OH groups and the like form electron traps. It is considered that, due to the potential generated by the electrons trapped in the traps, sputtering of the protective layer which is an insulating material proceeds.
Therefore, in the AC type plasma display device in which a thin dielectric layer composed of a low melting point glass is formed by the paste printing method, fluctuation of discharge start voltage or lowering of luminance would easily be generated due to the sputtering of the protective layer, resulting in difficulties on the basis of reliability.
The present invention has been made in consideration of the above circumstances. Accordingly, it is an object of the present invention to provide a plasma display device in which fluctuation of discharge start voltage and lowering of luminance would not easily occur, the burning phenomenon of the screen is suppressed, and which has excellent reliability and long life, and a method of producing the same.